From Rich Brownstein’s Holocaust Cinema Complete, pg. 70:

[T]he [Third Reich] built six camps specifically for slaughter, interchangeably known as “death camps,” “extermination camps” or “killing centers.” All six of these death camps were in occupied Poland: Chełmno, Belzec, Sobibór, Treblinka, Majdanek, and the camp system of Auschwitz/Birkenau. While some concentration camps had small gas chambers—Dachau, Stutthof, Mauthausen, Sachsenhausen, and Ravensbrück¹¹—extermination was the main business of the six death camps, even if labor ­sub-camps were part of a specific camp’s system, like at Auschwitz/Birkenau.

(Emphasis added.)

Since these were all in Poland, and the Soviets reached Poland whereas the Western Allies never did (otherwise there’d never be such a thing as the Polish People’s Republic), that means that the Soviets liberated all of these camps.

I hate to state the obvious, but scholarly citations like these are worth keeping in mind when anti-Bolsheviks inevitably say ‘you’re wrong’ to this sore point. Unfortunately, I predict that they are going to rescue their assumption by claiming that the Soviets merely captured the camps without liberating anybody (like this) and citing an Internet meme as the evidence. That, and referencing the Molotov Cocktease Pact: the single most important event in all of history right up until somebody murdered Charlie Kirk.